I bought the BCM from the dealer, managed 20% discount so I think it was less than £200 and then got £100 for my old one so wasn't to bad in the end.
The AFS addition with self leveller did take me a while. The worst bit was connecting to the CAN bus at the CAN bus controller.
After I had cut my knuckles to bits I later found out it is easier to get the CAN controller from the engine bay as detailed
HERE 
I bought the self leveller loom from Kufatec (Part No. 37139) but had to extend the wiring as I am not sure where they had intended to place the AFS controller.
If you have ACC on the car then the self levellers should already be installed.
I put more details of the parts needed in
THIS post.